Joker: One Operation Joker (2023)

During a fight with The Joker, Batman falls into a chemical vat that somehow turns him into a baby. Who is going to take care and help raise baby Batman? The Joker, that's who.

Written by Satoshi Miyagawa (Uchuu Senkan Tiramisù) and illustrated by Keisuke Gotou, this manga finds Batman transformed into a baby following an accidental fall into the same vat of chemicals that turned the Joker into his evil self.